Certain emerging vehicle designs can be propelled at least part of the time using only electrical energy. For example, hybrid electric vehicles (HEV), plug-in HEV (PHEV), and extended-range electric vehicles (EREV) each have one or more electric-only (EV) modes. An HEV and a PHEV may use an internal combustion engine as an energy source to supply torque to a set of drive wheels, while the EREV can use a smaller engine to power an electrical generator when more electricity is required. Battery electric vehicles (BEV) can be propelled exclusively in an EV mode, and therefore such vehicles do not require an engine.
Regardless of the vehicle embodiment, a rechargeable high-voltage battery pack can be used to alternatively store and deliver the substantial electrical energy needed for driving one or more traction motors of the vehicle's propulsion system. Depending on the design, the battery pack may be recharged when the vehicle is not in use by plugging the vehicle into an off-board power outlet. The battery pack of most EV-capable vehicles can also be charged when the vehicle is in operation using the energy captured during a regenerative braking event or other regenerative event.